U.S. patent application number 15/320820 was filed with the patent office on 2017-09-21 for detection of strain in fiber optics cables induced by narrow-band signals.
This patent application is currently assigned to Halliburton Energy Services, Inc.. The applicant listed for this patent is Halliburton Energy Services, Inc.. Invention is credited to David Andrew Barfoot, Andreas Ellmauthaler, Xinwei Lan, Yenny Natali Martinez, Leonardo de Oliveira Nunes.
Application Number | 20170268944 15/320820 |
Document ID | / |
Family ID | 57104103 |
Filed Date | 2017-09-21 |
United States Patent
Application |
20170268944 |
Kind Code |
A1 |
Nunes; Leonardo de Oliveira ;
et al. |
September 21, 2017 |
Detection Of Strain In Fiber Optics Cables Induced By Narrow-Band
Signals
Abstract
A method may include transmitting a narrowband signal into a
formation using a transmitter located in a wellbore. The narrowband
signal is modified by passage of through the formation and the
formation reflects at least a portion of the narrowband signal back
to the wellbore resulting in a modified narrowband signal having a
first frequency. The method also includes sensing the modified
narrowband signal with an optical waveguide positioned in the
wellbore, transmitting a source signal along a length of the
optical waveguide, and obtaining a backscattered return signal from
the optical waveguide. The backscattered return signal is sampled
at a second frequency that is less than the Nyquist rate of the
modified narrowband signal. The method further includes processing
the backscattered return signal to obtain an amplitude of the
modified narrowband signal.
Inventors: |
Nunes; Leonardo de Oliveira;
(Rio de Janeiro, BR) ; Barfoot; David Andrew;
(Houston, TX) ; Ellmauthaler; Andreas; (Rio de
Janeiro, BR) ; Martinez; Yenny Natali; (Houston,
TX) ; Lan; Xinwei; (Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Halliburton Energy Services, Inc. |
Houston |
TX |
US |
|
|
Assignee: |
Halliburton Energy Services,
Inc.
Houston
TX
|
Family ID: |
57104103 |
Appl. No.: |
15/320820 |
Filed: |
September 14, 2015 |
PCT Filed: |
September 14, 2015 |
PCT NO: |
PCT/US15/49977 |
371 Date: |
December 21, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 47/12 20130101;
E21B 47/005 20200501; E21B 49/0875 20200501; E21B 43/20 20130101;
E21B 47/113 20200501; E21B 49/08 20130101; E21B 49/00 20130101;
G01L 1/246 20130101 |
International
Class: |
G01L 1/24 20060101
G01L001/24; E21B 49/08 20060101 E21B049/08; E21B 47/12 20060101
E21B047/12; E21B 49/00 20060101 E21B049/00 |
Claims
1. A method, comprising: transmitting a narrowband signal into a
formation using a transmitter located in a wellbore, wherein the
narrowband signal is modified by passage through the formation and
the formation reflects at least a portion of the narrowband signal
back to the wellbore resulting in a modified narrowband signal
having a first frequency; sensing the modified narrowband signal
with an optical waveguide positioned in the wellbore; transmitting
a source signal along a length of the optical waveguide and
obtaining a backscattered return signal from the optical waveguide,
the backscattered return signal being sampled at a second frequency
that is less than a Nyquist rate of the modified narrowband signal;
and processing the backscattered return signal to obtain an
amplitude of the modified narrowband signal sensed with the optical
waveguide.
2. The method of claim 1, further comprising processing the
backscattered return signal to obtain the amplitude of the modified
narrowband signal independent of the first frequency of the
modified narrowband signal.
3. The method of claim 1, wherein sensing the modified narrowband
signal on the optical waveguide comprises inducing strain in the
optical waveguide via the modified narrowband signal.
4. The method of claim 1, further comprising processing the
backscattered return signal using interferometric phase modulation
techniques.
5. The method of claim 1, wherein processing the backscattered
return signal comprises filtering the backscattered return signal
using a low-pass filter having a cut off frequency equal to or
below the first frequency.
6. The method of claim 1, further comprising controlling the
transmitter to vary the amplitude of the modified narrowband
signal.
7. The method of claim 1, further comprising varying a frequency of
the narrowband signal transmitted into the formation and obtaining
the modified narrowband signal including a spectrum of
frequencies.
8. A system, comprising: a transmitter located in a wellbore and
generating a narrowband signal into a formation, wherein the
narrowband signal is modified by passage through the formation and
the formation reflects at least a portion of the narrowband signal
back to the wellbore resulting in a modified narrowband signal
having a first frequency; an optical waveguide positioned in the
wellbore to sense the modified narrowband signal; and an interface
to transmit a source signal along a length of the optical
waveguide, obtain a backscattered return signal from the optical
waveguide, sample the backscattered return signal at a second
frequency less than a Nyquist rate of the modified narrowband
signal, and process the backscattered return signal to obtain an
amplitude of the modified narrowband signal.
9. The system of claim 8, wherein the interface processes the
backscattered return signal to obtain the amplitude of the modified
narrowband signal independent of the first frequency of the
modified narrowband signal.
10. The system of claim 8, wherein the interface processes the
backscattered return signal using interferometric phase modulation
techniques.
11. The system of claim 8, wherein the interface filters the
backscattered return signal using a low-pass filter having a cut
off frequency equal to or below the first frequency.
12. The system of claim 8, wherein the interface controls the
transmitter to vary the amplitude of the modified narrowband
signal.
13. The system of claim 8, wherein the interface varies a frequency
of the narrowband signal transmitted into the formation to obtain
the modified narrowband signal including a spectrum of
frequencies.
14. A computer program product comprising a non-transitory computer
readable medium having computer readable computer program code
stored thereon that, when executed by a computer, configures the
computer to: transmit a narrowband signal into a formation using a
transmitter located in a wellbore, wherein the narrowband signal is
modified by passage through the formation and the formation
reflects at least a portion of the narrowband signal back to the
wellbore resulting in a modified narrowband signal having a first
frequency, the modified narrowband signal being sensed by an
optical waveguide positioned in the wellbore; program an interface
to transmit a source signal along a length of the optical waveguide
and obtain a backscattered return signal from the optical
waveguide, the backscattered return signal being sampled at a
second frequency that is less than a Nyquist rate of the modified
narrowband signal; and program the interface to process the
backscattered return signal to obtain an amplitude of the modified
narrowband signal.
15. The computer program product of claim 14, wherein the computer
is further configured to program the interface to process the
backscattered return signal such that the amplitude of the modified
narrowband signal is obtained independent of the first frequency of
the modified narrowband signal.
16. The computer program product of claim 14, wherein the computer
is further configured to program the interface to process the
backscattered return signal using interferometric phase modulation
techniques.
17. The computer program product of claim 14, wherein the computer
is further configured to program the interface to filter the
backscattered return signal using a low-pass filter having a cut
off frequency equal to or below the first frequency.
18. The computer program product of claim 14, wherein the computer
is further configured to program the interface to control the
transmitter to vary the amplitude of the modified narrowband
signal.
19. The computer program product of claim 14, wherein the computer
is further configured to vary a frequency of the narrowband signal
transmitted into the formation and obtain the modified narrowband
signal including a spectrum of frequencies.
Description
BACKGROUND
[0001] In the oil and gas industry, it can be required to measure
the characteristics and/or compositions of substances located at
remote subterranean locations and convey the results to the surface
for processing. For instance, it may be required to measure
chemical and/or physical properties of substances located in
subterranean hydrocarbon-bearing formations and convey the results
of the measurement over a long distance to the earth's surface.
These properties may vary continuously and, therefore, it is often
desired to measure these properties at a high frequency in order to
capture the variations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0002] The following figures are included to illustrate certain
aspects of the present disclosure, and should not be viewed as
exclusive embodiments. The subject matter disclosed is capable of
considerable modifications, alterations, combinations, and
equivalents in form and function, without departing from the scope
of this disclosure.
[0003] FIG. 1A illustrates an exemplary well monitoring and
measurement system that may employ the principles of the present
disclosure.
[0004] FIGS. 1B-1E each illustrate an exemplary configuration of
sensors in FIG. 1A.
[0005] FIG. 2 is a block diagram of an exemplary heterodyne
interrogation technique.
[0006] FIG. 3 is a block diagram of an exemplary homodyne
interrogation technique.
[0007] FIG. 4 illustrates an exemplary plot of the zero order
Bessel function of a signal incident on the optical waveguide of
FIG. 1A as a function of amplitude of the signal.
[0008] FIG. 5 is a flowchart of an exemplary method of calculating
an amplitude of the signal incident on the optical waveguide of
FIG. 1A.
[0009] FIG. 6 illustrates an exemplary processing system for
implementing one or more embodiments of the disclosure.
DETAILED DESCRIPTION
[0010] The present disclosure describes systems and methods of
calculating a gain of a narrowband signal independently of the
frequency of the narrowband signal.
[0011] Embodiments disclosed herein may permit de-coupling of the
frequency at which a property or characteristic of a component or a
substance in the wellbore is measured and the frequency at which
the measured property or characteristic is recovered (e.g.,
transmitted uphole) for analysis. As a result, it may be possible
to measure properties or characteristics of downhole substances
using high frequency instruments (e.g., ultrasonic measuring
instruments) and use low frequency instruments to transmit the
measured properties or characteristics uphole for further analysis.
The principles of the present disclosure may be utilized in a
variety of applications involving acoustic sensing, such as flow
detection and flow regime estimation, and applications involving
electromagnetic (EM) sensing, such as cement cure monitoring,
acoustic calipering, fluid identification, and downhole impedance
measurements. For instance, embodiments disclosed herein may permit
these applications to measure wellbore characteristics using high
frequency instruments, while the measured data may be retrieved for
processing using existing low frequency instruments. Those skilled
in the art will readily appreciate that the embodiments described
herein provide advanced methods of conducting a high frequency
examination of a wellbore without investing in new tools, new tool
hardware, or adaptations of existing tools.
[0012] Referring to FIG. 1A, illustrated is an exemplary well
monitoring and measurement system 100 that may employ the
principles of the present disclosure. It may be noted that the well
monitoring and measurement system 100 can be used in a land-based
operation as well as in any sea-based or sub-sea application
including a floating platform or sub-surface wellhead installation,
as generally known in the art. As illustrated in FIG. 1A, one or
more transmitters 102 (two shown) may be located downhole in a
wellbore 106 drilled in an earth formation 104. For instance, the
transmitters 102 may be located in an annulus 108 formed between
the wellbore 106 and a casing 110 secured therein via cement
113.
[0013] The transmitters 102 may be connected to each other and to
an interface 112 located on the earth's surface 103 via a control
cable 114. The transmitters 102 may be connected in series, in
parallel, or a combination thereof. The control cable 114 may take
different forms (e.g., a tubing encapsulated cable) and may include
embedded electrical conductors and/or optical waveguides (e.g.,
fibers) that transmit electrical power and control instructions to
the transmitters 102. The interface 112 may include a controller
116 to direct the operations of the transmitters 102.
[0014] Based on control signal(s) from the interface 112, the
transmitters 102 may each generate, either simultaneously or at
different times, a high frequency (e.g., greater than 100 kHz)
narrowband signal 120, the characteristics of which, such as
amplitude, frequency, and/or phase, are under user control via the
interface 112. In an embodiment, the signal 120 may be an
electromagnetic (EM) signal and may be generated by transmitters
102 that comprise coils external to the casing 110, as illustrated
in FIG. 1A. In another embodiment, the signal 120 may be an
acoustic signal and the transmitter 102 may be any acoustic signal
generator known in the art. The transmitters 102 may be positioned
in another wellbore, at the earth's surface, or in another
location. The scope of this disclosure is not limited to any
particular position of a transmitter, to any particular type of
transmitter, or to any particular technique for generating and
transmitting the signal 120 in the formation 104.
[0015] The formation 108 and/or the cement 113 may modify the
characteristics of the signal 120 (EM or acoustic). The modified
signal is detected by sensors 121 coupled to an optical waveguide
122 (such as, an optical fiber or an optical ribbon) positioned in
the annulus 108. In some embodiments, the optical waveguide 122 may
be attached external to the casing 110. In other embodiments, the
optical waveguide 122 including the sensors 121 may be deployed in
the casing 110 using wireline. In yet other embodiments, the
optical waveguide 122 may be positioned at a boundary of the cement
113 (e.g., adjacent the wall of the wellbore 106). In such
embodiments, the transmitters 120 may be located at an opposite
boundary of the cement 113 and the signal 120 may therefore
traverse the cement 113 before being detected by the sensors 121 of
the optical waveguide 122.
[0016] In an example, the frequency of the signal 120 emitted from
the transmitter 102 can be varied and a modified signal including a
spectrum of frequencies is obtained from the formation.
Illustrative examples of a substance or property of interest that
can be detected by the sensors 121 can include, for example,
chemical composition (e.g., identity and concentration in total or
of individual components), phase presence (e.g., gas, oil, water,
etc.), impurity content, pH, alkalinity, viscosity, density, ionic
strength, total dissolved solids, salt content (e.g., salinity),
porosity, opacity, bacteria content, total hardness, transmittance,
combinations thereof, state of matter (solid, liquid, gas,
emulsion, mixtures thereof, etc.), and the like.
[0017] FIGS. 1B-1E each illustrate an exemplary sensor 121
configuration, wherein an optical waveguide 122 is bonded or
otherwise attached to a material 126 which changes shape in
response to exposure to the EM signal 120 received from the
formation 104. As illustrated in FIGS. 1B-1D, the material 126 is
bonded to a section of the optical waveguide 122 longitudinally
between two fiber Bragg gratings 124. For example, an epoxy may be
used to adhere the optical waveguide 122 to the material 126. In
FIG. 1B, the material 126 is illustrated in the form of a wire or
rod. In FIG. 1C, the optical waveguide 122 is jacketed or coated
(surrounded) by the material 126. The material 126 is bonded or
otherwise adhered to an outer surface of the optical waveguide 122.
In FIG. 1D, the material 126 is illustrated as being planar in
form. In FIG. 1E, the optical waveguide 122 is wrapped about the
material 126, which is in cylindrical form. In this case, a radial
enlargement or contraction of the cylindrical material 126 will
change strain in the optical waveguide 122. The optical waveguide
122 may or may not be bonded to the material 126.
[0018] The material 126 can comprise a magnetostrictive material
(such as, Co, Fe, Ni, and iron-based alloys METGLAS.TM. and
TERFENOL-D.TM.) or an electrostrictive material (such as, lead
magnesium niobate (PMN), lead magnesium niobate-lead titanate
(PMN-PT), lead zirconate titanate (PZT), and lead lanthanum
zirconate titanate (PLZT)).
[0019] When the material 126 changes shape, the length of the
optical waveguide 122 attached to the material 126 is elongated or
contracted between the two Bragg gratings 124. Thus, a change in
strain (or change in length per unit length) is induced in the
optical waveguide 122 between the Bragg gratings 124 due to the
electromagnetic signal 120. The strain can be measured using a
variety of interferometry techniques.
[0020] Briefly, at the locations of sensors 121, a beam of highly
coherent light (such as a laser pulse) transmitted from a surface
location into the optical waveguide 122 is modulated by a change in
shape of the material 126 due to the electromagnetic field of the
EM signal 120. The modulated signal from each sensor 121 travels
along the optical waveguide 122 to a signal interrogator (118),
where a signal from each sensor 121 is extracted and demodulated
and the electromagnetic field strength at each sensor location
thereby is determined. In this manner, electromagnetic property of
the formation 104 can be mapped along the optical waveguide
122.
[0021] The Bragg gratings 124 can be useful in extracting a
modulated signal from each sensor 121. For example, in a wavelength
division multiplexing method, the Bragg gratings 124 can be used to
selectively reflect wavelengths of the beam of highly coherent
light so that the signal from one sensor can be distinguished from
others at the interrogator 118. The incident beam of light is
partially reflected at a first Bragg grating 124. The remaining
light travels through a cavity between the Bragg gratings 124 and
is again partly reflected at the second grating.
[0022] The reflected light from the two Bragg gratings 124 is
re-coupled into the same optical fiber and guided to an optical
monitor/interrogator 118 (FIG. 1A). There will be a change in phase
between the light reflected from the first Bragg grating 124 and
light reflected from the second Bragg grating, due to a strain
induced in the optical waveguide 122 bonded to material 126 between
the Bragg gratings 124.
[0023] In an exemplary application, the well monitoring and
measurement system 100 may be used for water flood monitoring.
Herein, a time-lapse measurement may be performed, in which
electric or magnetic fields (of the EM signal 120) are measured as
a function of time at each sensor 121. In a time-lapse measurement
system, a first measurement is performed at a time when there is no
flood and a second measurement is performed at a time in the
presence of flood, thereby generating a differential signal. As the
flood approaches closer to a sensor 121, the differential signal
gets larger. The intensity of the differential signal indicates a
distance to the flood front. The change in the electrical (or
magnetic) field induces a change in shape of the material 126,
which in turn induces a change in strain in the optical waveguide
122. The change in strain is measured using interferometry
techniques known in the art.
[0024] In the case where an acoustic signal 120 is emitted by the
transmitter 102, the sensors 121 may be absent. The interaction of
the optical waveguide 122 with the modified acoustic signal 120
received from the formation 104 or the cement 113 produces a strain
in the optical waveguide 122, which is translated into a change in
the phase of the backscattered light. Distributed acoustic sensing
(DAS) may be used to measure the strain change in the optical
waveguide 122 due to acoustic signal 120. Briefly, in DAS, an
optical monitor/interrogator 118 located at the interface 112 may
inject a beam of highly coherent light, such as a laser pulse, in
the optical waveguide 122. The strain change in the optical
waveguide 122 due to the acoustic signal 120 results in a change in
a path length and/or a change in the refractive index of the
optical waveguide 122, which causes an optical phase shift in the
backscattered return signal. The phase shift is detected and
analyzed by the optical monitor/interrogator 118 to determine the
location of the component or the substance in the wellbore 106.
[0025] DAS is discussed herein as an example of interferometric
phase modulation techniques used for measuring the strain change in
the optical waveguide 122. However, embodiments disclosed herein
are not limited thereto. Other interferometry techniques wherein
the information of interest is conveyed in the phase and the rate
at which the backscattered light is sampled (or, in other words,
the rate at which the change in strain is interrogated) is less
than the Nyquist rate (which is twice the frequency of the
narrowband signal 120 received at the optical waveguide 122 can
also be used. For example, in the case of DAS, the rate at which
the backscattered light is sampled is around 10 KHz, while the
frequency of the narrowband signal 120 is greater than 100 KHz
(Nyquist frequency rate being greater than 200 KHz).
[0026] The change in phase in the backscattered return signal due
to a change in strain caused by the high frequency narrowband
acoustic signal 120 received from the formation 104 or the cement
113 can be measured using a variety of detection methods, two of
which are disclosed herein below as the heterodyne detection method
and the homodyne detection method.
[0027] Referring to FIG. 2, an example of a heterodyne
interrogation scheme 200 that may be applied to the system 100 in
FIG. 1A is representatively illustrated. The heterodyne
interrogation scheme 200 may be implemented in the optical
monitor/interrogator 118. In the heterodyne interrogation scheme
200, each sensor 121 (FIGS. 1B-1E) comprises a pair of point
reflectors (e.g., Fiber Bragg Gratings, etc.), with the optical
waveguide 122 between the reflectors. The optical waveguide 122
between the reflectors undergoes a strain based on the parameter
being measured. The strain changes in the optical waveguide 122
between adjacent point reflectors causes difference in path length
of light transmitted in the optical waveguide 122 from a surface
location. The path length difference causes a phase change in the
back reflected light. In an embodiment, the sensors 121 may be
absent and optical waveguide 122 between a pair of "virtual"
reflectors undergoes strain with the distance between a "virtual"
reflector pair corresponding to half the length of the delay coil.
The "virtual" reflectors are not physical reflectors, but are
predetermined points along the optical waveguide 122 and a location
of which is determined by the time of flight of the backscattered
light. For instance, if a one meter separation is desired between
adjacent "virtual" reflectors, the backscattered light is sampled
at time instances corresponding to the time it takes for the
emitted pulse to advance two meters (round-trip distance). The
strain changes in the optical waveguide 122 between adjacent
"virtual" reflectors causes difference in path length of light
transmitted in the optical waveguide 122 from a surface location.
The path length difference causes a phase change in the
backscattered light. It should be noted that, for ease of
explanation, backscattered and back reflected may be used
interchangeably and indicate light being reflected back to the
monitor/interrogator 118 either due to the presence of the
"virtual" reflectors or point reflectors.
[0028] The optical waveguide 122 is interrogated with two pulses
f1, f2 that are spaced at twice the distance between the two
reflectors, such that the reflection of the two pulses f1, f2 will
arrive back at the optical monitor/interrogator 118 at the same
time.
[0029] In this example, to determine the phase measurement, the
pulses f1, f2 will be shifted in frequency relative to each other
by a frequency known as the intermediate frequency (IF). This
intermediate frequency will be extracted at the optical
monitor/interrogator 118 from, for instance, a square-law mixing of
the two reflected pulses f1, f2, which overlap.
[0030] Phase measurement is made using the IF or beat frequency.
The IF signal is shifted down to baseband by a pair of mixers 222,
224, which mix the signal from the optical receiver 220 with an IF
oscillator 212 generated sinusoid at the same IF.
[0031] One mixer 222 receives the IF oscillator 212 signal directly
and the second mixer 224 receives a 90 degree shifted version of
the oscillator signal. By doing this, the output of one mixer 222
contains the in-phase (I) measurement of the phase and the second
mixer 224 contains the quadrature (Q) measurement of the phase.
[0032] These I and Q signals are sampled simultaneously by two
analog to digital converters (not shown). Phase can be calculated
from the inverse tangent of Q/I. The mixing operations can also be
performed digitally if the signal is sampled at a sufficiently high
rate.
[0033] For providing the two pulses f1, f2, a pulse generator 204
receives light from a continuous wave (CW) source 202 and outputs a
pulse that is split into two paths with one path having a delay
coil 208 to provide the pulse separation. Additionally, one of the
paths contains a frequency shifting device 210 (for example, an
acousto-optic modulator) that shifts the light frequency by the
intermediate frequency. The pulse generator 204 is coupled to the
delay coil 208 and the frequency shifting device 210 via a coupler
206. The outputs of the delay coil 208 and the frequency shifting
device 210 are provided to another coupler 214 which is connected
to a circulator 216 that receives the backscattered return pulses
from the one or more sensors 121.
[0034] Referring to FIG. 3, an example of a homodyne interrogation
scheme 300 that may be applied to the system 100 is
representatively illustrated. The homodyne interrogation scheme 300
may be implemented in the optical monitor/interrogator 118. In the
homodyne interrogation scheme 300, a single optical interrogation
pulse is sent along the optical waveguide 122.
[0035] A pulse generator 204 receives light from a continuous wave
(CW) source 202 and outputs interrogation pulse to a circulator
216. The circulator 216 transmits the interrogation pulse to the
optical waveguide 122. As mentioned above, each sensor 121 on the
optical waveguide 122 comprises a pair of point reflectors (or
"virtual" reflectors, if present), with the optical waveguide 122
between the reflectors. The optical waveguide 122 undergoes a
strain based on the parameter being measured.
[0036] As the interrogation pulse travels through the optical
waveguide 122, imperfections in the optical waveguide 122 may cause
a portion of the interrogation pulse to be backscattered along the
optical waveguide 122. The backscattered return interrogation pulse
may travel back through the optical waveguide 122 until it reaches
the circulator 216 that redirects the backscattered return
interrogation pulse to a 1.times.2 coupler 302. The 1.times.2
coupler 302 splits the backscattered return interrogation pulse
such that half the backscattered return interrogation pulse travels
through the bottom path and half the backscattered return
interrogation pulse travels through the top path.
[0037] The delay coil 208 of length equal to twice the distance
between the two reflectors delays the pulse from the top path so
that, as the two pulses recombine at a 3.times.3 coupler 304, they
correspond to two distinct positions along the fiber constituting
one pair of point reflectors (or "virtual" reflectors, if present).
The overlapping pulses leave the 3.times.3 coupler 304 on the three
legs of the coupler 304. The phases of the pulses in the three legs
relative to each other are shifted differently for each leg of the
coupler 304 based on coupled mode theory. In this manner, the
3.times.3 coupler 304 will provide three interferometric signals.
For example, the first leg will contain the combined signals from
the reflectors. The second leg will contain the combined signals
shifted by +120 degrees. The third leg will contain the combined
signals shifted by -120 degrees.
[0038] The three legs of the coupler 304 effectively receive phase
delays (in addition to the actual phase delay between the light
reflected from each of the reflectors of the sensor 121) of 0,
+120, and -120 degrees. These three interferometric signals provide
enough phase diversity to calculate the phase difference between
the light reflected from each of the reflectors of the sensor 121
as follows:
I= {square root over (3)}*A-B
Q=A+B-2C
PHASE=ARCTAN(Q/I)
wherein A, B and C are the signals received from the three legs of
the coupler 304, respectively. In another embodiment, a 90-degree
optical hybrid that directly outputs the I/Q signals can be used
instead of 3.times.3 coupler 304.
[0039] For the sake of simplicity, the below-mentioned process has
been described with respect to a single transmitter 102; however,
it will be understood that the process is equally applicable to all
transmitters 102. It should also be noted that the below-mentioned
process takes into consideration the amplitude (or the energy) of
the modified signal 120 (FIG. 1A) sensed by the optical waveguide
122 (FIG. 1A). The modified signal 120 incident on the optical
waveguide 122 may be generally represented as:
x(t)=A.sub.E cos(.omega..sub.Et+.PHI..sub.E)
where A.sub.E, .PHI..sub.E, and .omega..sub.E are the amplitude,
phase, and frequency of the signal x(t), respectively. For ease of
explanation, it is assumed that the signal 120 emitted from the
transmitter 102 interacts with the formation 104 and/or the cement
113, and the amplitude of the signal 120 is modified based on the
interaction, while the frequency .omega..sub.E and phase
.PHI..sub.E, are assumed to be unchanged. Accordingly, the
amplitude of the signal emitted from the transmitter 102 is
different from the amplitude A.sub.E, while the frequency
.omega..sub.E and phase .PHI..sub.E, of the signal emitted from the
transmitter 102 are unchanged. The signal x(t) may induce strain
changes in the optical waveguide 122. As mentioned above, a highly
coherent light (e.g., a laser pulse) may be injected into the
optical waveguide 122 and may be either back-reflected due to
discrete points (e.g., Fiber Bragg Grating) placed along the fiber
or may be backscattered continuously due to Rayleigh
backscattering. The strain change caused by the signal x(t) (or by
the material 126 (FIGS. 1B-1E) attached to the optical waveguide
122) may provoke a phase change in the backscattered (or
back-reflected) return signal. The backscattered return signal may
be detected by the optical monitor/interrogator 118. For the sake
of explanation, we assume a homodyne detection of the backscattered
return signal, although the explanation below is equally applicable
to heterodyne detection of the backscattered return signal. The
backscattered return signal may be represented as:
y(t)=Q(t)+jI(t)=A.sub.Oe.sub.jx(t)=A.sub.Oe.sup.j(A.sup.E.sup.cos(.omega-
..sup.E.sup.t+.PHI..sup.E.sup.))
where A.sub.O is the complex optical gain of the signal y(t).
[0040] The signal y(t) can be written in the following form:
y ( t ) = A O n j n J n ( A E ) e j ( n .omega. E t + .PHI. E )
##EQU00001##
where J.sub.n represents the n.sup.th order Bessel function of the
signal x(t). From the equation above, it may be noted that the
spectrum of the detected signal y(t) may be composed of lines on
.omega..sub.E and its multiples, the amplitudes of which may be
determined by the Bessel function of appropriate order of amplitude
A.sub.E. The signal y(t) may be filtered using a low-pass filter
having a cut-off frequency at or about .omega..sub.E and the
following signal may be obtained:
y.sub.DCc(t)=A.sub.OJ.sub.O(A.sub.E)
which represents a number in the complex plane (or, z-plane),
assuming the optical gain A.sub.O is constant.
[0041] In order to correctly estimate the amplitude A.sub.E, it may
be required to estimate the complex optical gain A.sub.O. In an
embodiment, the optical monitor/interrogator 118 may issue a
command to the controller 116 to switch off the transmitter 102.
The optical monitor/interrogator 118 may measure amplitude of
signal y.sub.DC while the transmitter 102 is off. The optical
monitor/interrogator 118 may then issue another command to the
controller 116 to turn on the transmitter 102, and may measure the
amplitude of the signal y.sub.DC while the transmitter 102 is ON.
The optical monitor/interrogator 118 may then calculate a
difference in the amplitudes to obtain an estimate of the complex
optical gain A.sub.O.
[0042] FIG. 4 illustrates a sample plot of the zero order Bessel
function J.sub.O(A.sub.E) as a function of signal amplitude
A.sub.E, wherein it may be seen that J.sub.O is not a monotonic
function. Referring to FIG. 4, it may be possible to measure
amplitude A.sub.E unequivocally if the amplitude A.sub.E is below a
certain value. Since the operation of the transmitter 102 can be
controlled, it may be possible to control the transmitter 102
(e.g., by reducing its transmission power) such that the received
amplitude A.sub.E of the signal x(t) is decreased. For instance,
from the illustrated plot, for the zero order Bessel function
J.sub.O(A.sub.E) value of "0," the amplitude A.sub.E may be 2.3,
5.5, and 8.3, approximately. In order to obtain an unambiguous
value of amplitude A.sub.E of the received signal x(t), the
transmitter 102 may be controlled such that amplitude A.sub.E may
be reduced to less than "2." Thus, it may be seen that unambiguous
values of the zero order Bessel function J.sub.O(A.sub.E) may be
obtained for an amplitude A.sub.E value less than around "2".
[0043] As is seen, the equation for y.sub.DC(t) above does not
contain any term representing the frequency .omega..sub.E of the
signal x(t) incident on the optical waveguide 122. It may thus be
determined that the amplitude A.sub.E may be obtained independently
of the frequency .omega..sub.E of the incident signal x(t).
Accordingly, it may be possible to measure a property of a
substance in the wellbore using a high frequency (e.g., greater
than 100 KHz) tool and sample the measured property at a lower
frequency (e.g., less than 10 KHz).
[0044] FIG. 5 is a flowchart of an exemplary method 500 of
calculating an amplitude of the signal incident on the optical
waveguide of FIG. 1A. The method 500 may include transmitting a
narrowband signal into a formation using a transmitter located in a
wellbore, as at 502. The narrowband signal is modified by passage
through the formation and the formation reflects at least a portion
of the narrowband signal back to the wellbore resulting in a
modified narrowband signal having a first frequency. The method 500
may also include sensing the modified narrowband signal with an
optical waveguide positioned in the wellbore, as at 504, and
transmitting a source signal along a length of the optical
waveguide and obtaining a backscattered return signal from the
optical waveguide, as at 506. The backscattered return signal is
sampled at a second frequency that is less than twice the Nyquist
rate of the modified narrowband signal. The method 500 may further
include processing the backscattered return signal to obtain an
amplitude of the modified narrowband signal sensed with the optical
waveguide, as at 508.
[0045] FIG. 6 shows an illustrative processing system 600 for
implementing one or more embodiments of the disclosure. The system
600 may include a processor 610, a memory 620, a storage device
630, and an input/output device 640. Each of the components 610,
620, 630, and 640 may be interconnected, for example, using a
system bus 650. The processor 610 may be processing instructions
for execution within the system 600. In some embodiments, the
processor 610 is a single-threaded processor, a multi-threaded
processor, or another type of processor. The processor 610 may be
capable of processing instructions stored in the memory 620 or on
the storage device 630. The memory 620 and the storage device 630
can store information within the computer system 600.
[0046] The input/output device 640 may provide input/output
operations for the system 600. In some embodiments, the
input/output device 640 can include one or more network interface
devices, e.g., an Ethernet card; a serial communication device,
e.g., an RS-232 port; and/or a wireless interface device, e.g., an
802.11 card, a 3G wireless modem, or a 4G wireless modem. In some
embodiments, the input/output device can include driver devices
configured to receive input data and send output data to other
input/output devices, e.g., keyboard, printer and display devices
660. In some embodiments, mobile computing devices, mobile
communication devices, and other devices can be used.
[0047] In accordance with at least some embodiments, the disclosed
methods and systems related to scanning and analyzing material may
be implemented in digital electronic circuitry, or in computer
software, firmware, or hardware, including the structures disclosed
in this specification and their structural equivalents, or in
combinations of one or more of them. Computer software may include,
for example, one or more modules of instructions, encoded on
computer-readable storage medium for execution by, or to control
the operation of, a data processing apparatus. Examples of a
computer-readable storage medium include non-transitory medium such
as random access memory (RAM) devices, read only memory (ROM)
devices, optical devices (e.g., CDs or DVDs), and disk drives.
[0048] The term "data processing apparatus" encompasses all kinds
of apparatus, devices, and machines for processing data, including
by way of example a programmable processor, a computer, a system on
a chip, or multiple ones, or combinations, of the foregoing. The
apparatus can include special purpose logic circuitry, e.g., an
FPGA (field programmable gate array) or an ASIC (application
specific integrated circuit). The apparatus can also include, in
addition to hardware, code that creates an execution environment
for the computer program in question, e.g., code that constitutes
processor firmware, a protocol stack, a database management system,
an operating system, a cross-platform runtime environment, a
virtual machine, or a combination of one or more of them. The
apparatus and execution environment can realize various different
computing model infrastructures, such as web services, distributed
computing, and grid computing infrastructures.
[0049] A computer program (also known as a program, software,
software application, script, or code) can be written in any form
of programming language, including compiled or interpreted
languages, declarative, or procedural languages. A computer program
may, but need not, correspond to a file in a file system. A program
can be stored in a portion of a file that holds other programs or
data (e.g., one or more scripts stored in a markup language
document), in a single file dedicated to the program in question,
or in multiple coordinated files (e.g., files that store one or
more modules, sub programs, or portions of code). A computer
program may be executed on one computer or on multiple computers
that are located at one site or distributed across multiple sites
and interconnected by a communication network.
[0050] Some of the processes and logic flows described in this
specification may be performed by one or more programmable
processors executing one or more computer programs to perform
actions by operating on input data and generating output. The
processes and logic flows may also be performed by, and apparatus
may also be implemented as, special purpose logic circuitry, e.g.,
an FPGA (field programmable gate array) or an ASIC (application
specific integrated circuit).
[0051] Processors suitable for the execution of a computer program
include, by way of example, both general and special purpose
microprocessors and processors of any kind of digital computer.
Generally, a processor will receive instructions and data from a
read-only memory or a random access memory or both. A computer
includes a processor for performing actions in accordance with
instructions and one or more memory devices for storing
instructions and data. A computer may also include, or be
operatively coupled to receive data from or transfer data to, or
both, one or more mass storage devices for storing data, e.g.,
magnetic, magneto optical disks, or optical disks. However, a
computer may not have such devices. Devices suitable for storing
computer program instructions and data include all forms of
non-volatile memory, media and memory devices, including by way of
example semiconductor memory devices (e.g., EPROM, EEPROM, flash
memory devices, and others), magnetic disks (e.g., internal hard
disks, removable disks, and others), magneto optical disks, and
CD-ROM and DVD-ROM disks. The processor and the memory can be
supplemented by, or incorporated in, special purpose logic
circuitry.
[0052] To provide for interaction with a user, operations may be
implemented on a computer having a display device (e.g., a monitor,
or another type of display device) for displaying information to
the user and a keyboard and a pointing device (e.g., a mouse, a
trackball, a tablet, a touch sensitive screen, or another type of
pointing device) by which the user can provide input to the
computer. Other kinds of devices can be used to provide for
interaction with a user as well; for example, feedback provided to
the user can be any form of sensory feedback, e.g., visual
feedback, auditory feedback, or tactile feedback; and input from
the user can be received in any form, including acoustic, speech,
or tactile input. In addition, a computer can interact with a user
by sending documents to and receiving documents from a device that
is used by the user; for example, by sending web pages to a web
browser on a user's client device in response to requests received
from the web browser.
[0053] A computer system may include a single computing device, or
multiple computers that operate in proximity or generally remote
from each other and typically interact through a communication
network. Examples of communication networks include a local area
network ("LAN") and a wide area network ("WAN"), an inter-network
(e.g., the Internet), a network comprising a satellite link, and
peer-to-peer networks (e.g., ad hoc peer-to-peer networks). A
relationship of client and server may arise by virtue of computer
programs running on the respective computers and having a
client-server relationship to each other.
[0054] Embodiments disclosed herein include:
[0055] A. A method that includes transmitting a narrowband signal
into a formation using a transmitter located in a wellbore, wherein
the narrowband signal is modified by passage through the formation
and the formation reflects at least a portion of the narrowband
signal back to the wellbore resulting in a modified narrowband
signal having a first frequency, sensing the modified narrowband
signal with an optical waveguide positioned in the wellbore,
transmitting a source signal along a length of the optical
waveguide and obtaining a backscattered return signal from the
optical waveguide, the backscattered return signal being sampled at
a second frequency that is less than the Nyquist rate of the
modified narrowband signal, and processing the backscattered return
signal to obtain an amplitude of the modified narrowband signal
sensed with the optical waveguide.
[0056] B. A system that includes a transmitter located in a
wellbore and generating a narrowband signal into a formation,
wherein the narrowband signal is modified by passage through the
formation and the formation reflects at least a portion of the
narrowband signal back to the wellbore resulting in a modified
narrowband signal having a first frequency, an optical waveguide
positioned in the wellbore to sense the modified narrowband signal,
and an interface to transmit a source signal along a length of the
optical waveguide, obtain a backscattered return signal from the
optical waveguide, sample the backscattered return signal at a
second frequency less than the Nyquist rate of the modified
narrowband signal, and process the backscattered return signal to
obtain an amplitude of the modified narrowband signal.
[0057] C. A computer program product that includes a non-transitory
computer readable medium having computer readable computer program
code stored thereon that, when executed by a computer, configures
the computer to transmit a narrowband signal into a formation using
a transmitter located in a wellbore, wherein the narrowband signal
is modified by passage through the formation and the formation
reflects at least a portion of the narrowband signal back to the
wellbore resulting in a modified narrowband signal having a first
frequency, the modified narrowband signal being sensed by an
optical waveguide positioned in the wellbore, program an interface
to transmit a source signal along a length of the optical waveguide
and obtain a backscattered return signal from the optical
waveguide, the backscattered return signal being sampled at a
second frequency that is less than the Nyquist rate of the modified
narrowband signal, and program the interface to process the
backscattered return signal to obtain an amplitude of the modified
narrowband signal.
[0058] Each of embodiments A, B, and C may have one or more of the
following additional elements in any combination: Element 1:
further comprising processing the backscattered return signal to
obtain the amplitude of the modified narrowband signal independent
of the first frequency of the modified narrowband signal. Element
2: wherein sensing the modified narrowband signal on the optical
waveguide comprises inducing strain in the optical waveguide via
the modified narrowband signal. Element 3: further comprising
processing the backscattered return signal using interferometric
phase modulation techniques. Element 4: wherein processing the
backscattered return signal comprises filtering the backscattered
return signal using a low-pass filter having a cut off frequency
equal to or below the first frequency. Element 5: further
comprising controlling the transmitter to vary the amplitude of the
modified narrowband signal. Element 6: further comprising varying a
frequency of the narrowband signal transmitted into the formation
and obtaining the modified narrowband signal including a spectrum
of frequencies.
[0059] Element 7: wherein the interface processes the backscattered
return signal to obtain the amplitude of the modified narrowband
signal independent of the first frequency of the modified
narrowband signal. Element 8: wherein the interface processes the
backscattered return signal using interferometric phase modulation
techniques. Element 9: wherein the interface filters the
backscattered return signal using a low-pass filter having a cut
off frequency equal to or below the first frequency. Element 10:
wherein the interface controls the transmitter to vary the
amplitude of the modified narrowband signal. Element 11: wherein
the interface varies a frequency of the narrowband signal
transmitted into the formation to obtain the modified narrowband
signal including a spectrum of frequencies.
[0060] Element 12: wherein the computer is further configured to
program the interface to process the backscattered return signal
such that the amplitude of the modified narrowband signal is
obtained independent of the first frequency of the modified
narrowband signal. Element 13: wherein the computer is further
configured to program the interface to process the backscattered
return signal using interferometric phase modulation techniques.
Element 14: wherein the computer is further configured to program
the interface to filter the backscattered return signal using a
low-pass filter having a cut off frequency equal to or below the
first frequency. Element 15: wherein the computer is further
configured to program the interface to control the transmitter to
vary the amplitude of the modified narrowband signal. Element 16:
wherein the computer is further configured to vary a frequency of
the narrowband signal transmitted into the formation and obtain the
modified narrowband signal including a spectrum of frequencies.
[0061] Therefore, the disclosed systems and methods are well
adapted to attain the ends and advantages mentioned as well as
those that are inherent therein. The particular embodiments
disclosed above are illustrative only, as the teachings of the
present disclosure may be modified and practiced in different but
equivalent manners apparent to those skilled in the art having the
benefit of the teachings herein. Furthermore, no limitations are
intended to the details of construction or design herein shown,
other than as described in the claims below. It is therefore
evident that the particular illustrative embodiments disclosed
above may be altered, combined, or modified and all such variations
are considered within the scope of the present disclosure. The
systems and methods illustratively disclosed herein may suitably be
practiced in the absence of any element that is not specifically
disclosed herein and/or any optional element disclosed herein.
While compositions and methods are described in terms of
"comprising," "containing," or "including" various components or
steps, the compositions and methods can also "consist essentially
of" or "consist of" the various components and steps. All numbers
and ranges disclosed above may vary by some amount. Whenever a
numerical range with a lower limit and an upper limit is disclosed,
any number and any included range falling within the range is
specifically disclosed. In particular, every range of values (of
the form, "from about a to about b," or, equivalently, "from
approximately a to b," or, equivalently, "from approximately a-b")
disclosed herein is to be understood to set forth every number and
range encompassed within the broader range of values. Also, the
terms in the claims have their plain, ordinary meaning unless
otherwise explicitly and clearly defined by the patentee. Moreover,
the indefinite articles "a" or "an," as used in the claims, are
defined herein to mean one or more than one of the elements that it
introduces. If there is any conflict in the usages of a word or
term in this specification and one or more patent or other
documents that may be incorporated herein by reference, the
definitions that are consistent with this specification should be
adopted.
[0062] As used herein, the phrase "at least one of" preceding a
series of items, with the terms "and" or "or" to separate any of
the items, modifies the list as a whole, rather than each member of
the list (i.e., each item). The phrase "at least one of" allows a
meaning that includes at least one of any one of the items, and/or
at least one of any combination of the items, and/or at least one
of each of the items. By way of example, the phrases "at least one
of A, B, and C" or "at least one of A, B, or C" each refer to only
A, only B, or only C; any combination of A, B, and C; and/or at
least one of each of A, B, and C.
* * * * *